In Germany this situation changed irrevocably in 1941 when AEG
engineers von Braunmühl and Weber stumbled across AC tape bias, where
the addition of an inaudible high-frequency tone resulted in a
striking improvement in sound quality ? something that was radical
enough to be discernible in prerecorded German AM broadcasts, if the
BBC's Caversham Park wartime monitoring reports are to be credited.
In fact, this is not so hard to believe, as the generous bandwidth of
national AM channels in the 1930s and '40s offered a far higher level
of AM fidelity than we're used to today. Nazi speeches aside, the
technical leap forward was most glaringly obvious in prerecorded
broadcasts by the likes of Fürtwängler and the Berlin Philharmonic,
as recent CD reissues have adequately confirmed.
While Jack Mullen may have been able to kickstart Ampex by sending
home a couple of these liberated machines in bits via the no-doubt
bemused Army Post Office, the final broadcast requirement for tape ?
superior editability ? was only really achieved when the notoriously
fragile German acetate-backed "paper" tape could be abandoned in
1947-48 in favor of 3M's new, sturdier #111 stock. From that moment
on tape was definitely superior to disc as a studio medium, even if
Bing's transcriptions were still pressed up as discs.